can you melt down DAP without it separating after mixing?If it were solid, a nice soluble form would be DAP. 160 kg/ha gives you 30 kg of N and 74 kg of P (enough P for the entire crop).
I will be fitting a liquid kit to my next drill & it will use the same N+S liquid I use for foliar treatment for the only reason being simple logistics. I'd have a bit of P in it too if I had the spare tanks. I prefer to keep my soil P indices above 2 so the crop can get what it needs fairly quickly.